1. Technical Field
The present invention relates to a method of controlling signal power level in a wireless communication system and a Bluetooth device for performing the same.
2. Discussion of the Related Art
Bluetooth is a radio communication protocol that allows electronic devices to communicate wirelessly within a short range. Bluetooth transceivers are embedded in portable devices such as mobile phones, laptop computers, MP3 players, game consoles, printers, home network devices, network access points, peripheral devices, etc., thereby enabling such devices to communicate wirelessly.
According to the Bluetooth specification version 1.0, a copy of which is herein incorporated by reference, the Bluetooth protocol has a maximum data transmission rate of 1 Mbps and a maximum transmission distance of 10 m-100 m. In addition, Bluetooth operates in a radio frequency (RF) environment (e.g., at 2.4 GHz) having a large quantity of noise.
Bluetooth uses a frequency hopping technique having a hopping rate of up to 1600 hops/sec to transmit/receive data. This frequency hopping technique divides the given frequency band into 79 hopping channels, which are separated from one another in intervals of 1 MHz (e.g., 2.402 MHz-2.480 MHz). The channels to which Bluetooth signals are allocated are switched at a high rate, such as 1600 hops/sec to reduce the effects of multi-channel interference and narrow-band impulse-based noise.
Devices used in a Bluetooth system are synchronized before communicating with each other. In particular, after Bluetooth equipped devices are synchronized via an RF link using their link managers, a communication channel is allocated from one of, for example, the 79 hopping channels, and the devices are able to communicate with each other transmitting, for example, data containing characters and voice.
The Bluetooth system typically consumes a small amount of power. Thus, portable devices such as a mobile phone are typically used in the Bluetooth system. The Bluetooth specifications define a receiver signal strength indicator (RSSI) measurement or a power control link manager protocol (LMP) message for controlling the power of signals to be transmitted in the Bluetooth system. In addition, the RSSI measurement is used to control a power level of signals transmitted from a remote Bluetooth device to a local Bluetooth device so that the local Bluetooth device can receive the signals transmitted from the remote Bluetooth device. Some Bluetooth devices, however, do not support the RSSI measurement or the power control LMP message.
According to the Bluetooth specifications, a local Bluetooth device transmits the power control LMP message only when the strength of the received signals is between a RealLowerLimit and an RSSILowerLimit or between an RSSIUpperLimit and a RealUpperLimit. The RealLowerLimit is a minimum power level limit that the local Bluetooth device may receive a packet without failure, and the RealUpperLimit is maximum power level limit that the local Bluetooth device may receive a packet without failure.
When the strength of the received signals is between the RSSILowerLimit and the RSSIUpperLimit, the local Bluetooth device does not transmit the power control LMP message to the remote Bluetooth device. Accordingly, the remote Bluetooth device maintains a previous signal power level for transmitting the signal to the local Bluetooth device.
Therefore, power dissipates when the link between Bluetooth devices is satisfactory or when two Bluetooth devices are very close to each other. In addition, interference between the Bluetooth devices within a predetermined distance increases. However, when the link between the Bluetooth devices is not satisfactory, communication channels are unnecessarily used due to signal retransmission causing an overload between the local and remote Bluetooth devices.